As one of conventional systems for suppressing an excitation rush current generated when a transformer is turned on by a three-phase power supply, there is known a phase control turn-on system for turning on a breaker in a specific phase of the three-phase power supply (see, for example, Patent Literature 1 described below).
Patent Literature 1 describes a transformer-excitation-rush-current suppressing device in a three-phase circuit including a three-phase transformer including star-connected primary windings having a grounded neutral point and delta-connected secondary or tertiary windings, and a three-phase breaker that allows the three-phase transformer to be turned on by a three-phase power supply and disconnected from the three-phase power supply. The transformer-excitation-rush-current suppressing device suppresses an excitation rush current that is a transient current generated in the three-phase transformer when the three-phase breaker is turned on. The transformer-excitation-rush-current suppressing device closes any one of three phases as a closing first phase earlier than the remaining two phases and, after a time set in advance elapses since the closing first phase is closed, closes the remaining two phases. Concerning the closing first phase, a phase of 0 degree of any reference phase is set as a reference point, and a closing phase in which a turn-on magnetic flux error which is the absolute value of a maximum error between a residual magnetic flux value and a steady magnetic flux value at a turn-on point is the smallest is calculated on the basis of a residual magnetic flux of the closing first phase and a pre-arc characteristic and a closing time variation characteristic of the three-phase breaker calculated in advance. The calculated closing phase is set as a target closing phase of the closing first phase. Concerning the remaining two phases, with the phase of 0 degree of the reference phase set as the reference point, a closing phase in which the turn-on magnetic flux error is the smallest when the residual magnetic flux is 0 is calculated on the basis of the pre-arc characteristic and the closing time variation characteristic of the three-phase breaker calculated in advance. The calculated closing phase is set as a target closing phase of the remaining two phases. A time obtained by totaling a time from the reference point to the target closing phase of the remaining two phases and a delay time equivalent to an integer multiple of a cycle of the three-phase power supply set in advance is set as a target closing time of the remaining two phases.